The use of such thickeners in softening compositions makes it possible to improve their rheological profile and therefore to modify the properties of the softening formulation. Moreover, the role of the softener is to provide a much more pleasant feel by lubrication of the animal textile fibres (wool in particular) and plant textile fibres (cotton) and of the synthetic fibres after treatment. It also provides antistatic properties by reducing the friction between fibres, it provides sensations of freshness by virtue of the fragrances incorporated, and it makes it possible to bring out the colours and to facilitate ironing.
In the remainder of the description and in the claims, the expression “thickener” is intended to mean, without implied distinction, thickener and/or stabilizer
Document WO 90/12862 describes a softening composition comprising a cationic polymer which acts as a thickener. This polymer is very lightly crosslinked in the presence of from 5 to 45 ppm of a crosslinking agent comprising polyethylenic functions.
Document U.S. Pat. No. 6,864,223 describes a softening composition containing polymers of the same type, but which are crosslinked to a greater extent (70-300 ppm) and combined with a softener of quaternized ester type and with a fragrance.
The publication Research Disclosure No. 429116, from January 2000, relates to the preparation of cationic polymers in inverse emulsions and to their use as thickeners in various compositions, such as, for example, for fabric softeners.
Document WO 2005/053748 by the Applicant describes heavily crosslinked cationic polymers (>300 ppm), used as thickeners of aqueous compositions.
Patent application PCT/EP2009/050077, still by the Applicant, describes cationic polymers, in the form of an inverse emulsion, which are very heavily crosslinked and have a maximum insoluble material content of 15%. These polymers can be used in softening compositions.
Document WO 97/36981 describes softening compositions which are stable and viscous by combining an acrylic thickener, as described in document WO 90/12862, and an associative polymer of ethoxy/propoxy (EO/PO) surfactant type.
Documents EP 0 172 723 and EP 0 172 724 describe polymer compositions and an inverse emulsion polymerization process for preparing anionic or cationic, linear or crosslinked polymers containing hydrophobic groups having more than 8 carbon atoms.
Document US 2004/052746 describes in particular a softening composition comprising a polymer obtained by polymerization of the following four monomers:                a vinyl monomer having a cationic or neutral amine group;        a nonionic and hydrophobic vinyl monomer;        an associative vinyl monomer; and        a semihydrophobic vinyl surfactant monomer.        
In addition, it is specified that the presence of the semihydrophobic vinyl surfactant monomer is essential for the stability of the emulsions comprising this copolymer.
Document EP 1 099 749 describes a softening composition comprising a neutral copolymer obtained by polymerization of:                a monomer based on acrylic acid or methacrylic acid;        a vinyl monomer; and        an associative monomer.        
Document WO 2005/087188 describes an anti-adhesive substance for cosmetic preparations comprising the neutral terpolymer obtained in particular by polymerization of:                dimethylaminoethyl methacrylate;        ethyl acrylate; and        beheneth-25 methacrylate.        
Document WO 97/22640 describes a foaming agent comprising a terpolymer obtained by polymerization of:                a cationic monomer (DADMAC);        a vinyl monomer comprising an amide group; and        a vinyl monomer having a hydrophobic group and also a hydrophilic group.        
Document U.S. Pat. No. 4,454,060 describes a liquid detergent composition comprising a copolymer that can be prepared from:                an acrylamide-based monomer;        a cationic monomer; and        a monomer comprising a hydrophobic group.        
Document EP 1 449 862 describes the use of a cationic polymer as a thickener in a cosmetic or pharmaceutical composition, as a thickener for printing pastes for the textile industry, as a thickener for industrial or household detergents or else in the petroleum industry. Said polymer comprises a cationic monomer, a neutral monomer and a nonionic surfactant monomer.
It should, however, be noted that documents WO 2005/087188, WO 97/22640, U.S. Pat. No. 4,454,060 and EP 1 449 862 do not therefore relate to softening compositions.
Although the thickeners used in the fabric softener compositions described in the prior art certainly make it possible to thicken the compositions, there is, however, a need to control the rheological profile of the formulation better and to obtain an increased stability of the composition.
Indeed, the viscosity of such a composition is influenced by a very large number of parameters:                variable concentrations of softener (diluted to concentrated form);        complex processes for use (agitation, temperature, batch or continuous, etc.);        numerous regional specificities (South America, Asia, Europe, North America).        
It is also necessary to improve the compatibility between the thickening polymers and the softeners and therefore the stability of the composition.
Document WO 2008/036587 describes an antiperspirant composition comprising a modified hydrophobic cationic polymer. This polymer can be obtained by polymerization of the following four monomers:                a vinyl monomer;        a hydrophobic nonionic vinyl monomer;        an associative vinyl monomer; and        a semihydrophobic surfactant vinyl monomer.        
The present invention proposes to solve in particular the following technical problems:                improvement of the stability of the softening compositions;        increase in the thickening capacity of the polymers in the softening compositions, thus making it possible to significantly reduce the amount of polymer;        improvement of the rheological profile, regardless of the concentration of the softener.        